Recovery of polyphenols from agri-food by-products with whey protein stabilised colloidal gas aphrons

Valorisation of food waste and losses is of great importance to achieve sustainability and a way to allocate these materials at a higher level in the waste management hierarchy. Moreover, food by-products are sources of important molecules such as proteins and polyphenols. In the present study, colloidal gas aphrons (CGA), surfactant stabilized micro bubbles with separation properties, are generated for the first time from whey protein (CGA(WPI) and investigated for separation and stabilisation of polyphenols extracted from fruit processing by-products. The capacity of whey protein to generate CGA was measured and compared against CGA made of Tween 20. Phenolic extracts were obtained using ethanol and methanol for comparison; CGA were then applied to hydroalcoholic extracts. The recovery of polyphenols, antioxidant activity and anthocyanins stability under storage were then investigated. Additionally, the encapsulation through nano spray drying and in vitro digestion of a raw grape marc extract using whey protein and pectin was also assessed. The main outcome was the production of stable CGA(WPI), with comparable characteristics to those of CGA(Tween 20). The application of CGA to various hydroalcoholic extracts showed that the type of polyphenols and surfactant influenced the recovery yields, especially anthocyanins, possibly due to near-neutral pH. CGA(WPI) and CGA(Tween 20) displayed a stabilisation effect for most of the evaluated anthocyanins. Both, separation and stabilisation, could be linked to the hydrophobic interactions occurring between surfactants and polyphenols, as well as hydrogen bonding in the case of CGA(WPI). Finally, the encapsulation through nano-spray drying led to microparticles with reduced size compared to spray drying, and improved bioaccessibility of polyphenols after in vitro digestion. In conclusion, CGA(WPI) demonstrated to be effective in the separation of polyphenols, and a novel way to use whey protein and fruit by-products. Moreover, it opens the perspective for CGA to be used as a pre-formulation step for the development of functional foods and nutraceuticals